1. Field of the Invention
This invention relates generally to rotary seals. In particular the invention relates to normally non-contacting seals coaxially disposed about a rotating member, which when actuated by hydraulic pressure, seal about an external cylindrical surface of the rotating member. More particularly, the invention relates to a pressure actuated hydraulic seal for communicating hydraulic fluid to a valve actuator for opening or closing a flow path through the rotating member.
2. Description of the Prior Art
Prior art machanisms for sealing between a stationary member and a rotating member while applying pressurized hydraulic fluid from the stationary member to the rotating member have generally required continuous contact of one or more seals between the stationary member and the rotating member. One such arrangement is illustrated in U.S. Pat. No. 4,339,108 to Daniluk for an upper kelly valve. Daniluk shows a stationary ported member sealed with respect to a rotating member for directing hydraulic fluid to the rotating member in order to control a valve in the flow path of the rotating member. The seals between the stationary member and the rotating member are continuously contacting O-ring seals which may suffer thermal runaway under requirements of high rpm and pressure necessary for such kelly valves.
As the Daniluk apparatus illustrates, standard hydraulic seals for sealing between a stationary member and a rotating member are in constant contact with the sealing surface of the rotating member. Relative motion of the stationary member with the rotating member results in wear on the seal and the sealing surface of the rotating member along with frictional heating. As surface speeds increase, the frictional heating can be sufficient to degrade and eventually destroy the seal through overheating.